The present invention relates to a cement sheet product which contains asbestos or other reinforcing fibers.
By way of background, in the past asbestos-cement compositions have been formed into sheets for subsequent formation into such products as siding shingles, flat sheets, corrugated sheet products, and the like. These sheets generally contained Type I Portland cement binder in an amount of about 58%, silica and/or filler in an amount of about 27%, and asbestos fibers in an amount of about 15%. The products had many desirable qualities including high strength, exterior durability, easy application, and the ability to be colored in various colors. In addition, products containing asbestos have a dimensional movement as follows when going from a saturated to a bone dry state: Normal cure --0.035--0.045 inches/foot, Autoclaved --0.018--0.024 inches/foot. These ranges are well documented in the asbestos-cement products industry. It is also well known that the lower the dimensional movement, the more stable the product, and the more resistant the product is to cracking or warping in extreme cases of outdoor exposure where relative humidity and temperature conditions vary considerably. However, in recent years, governmental regulations have restricted the use of asbestos. Therefore, attempts have been made to find substitutes for asbestos. One such attempt is disclosed in U.S. Pat. No. 4,040,851 which utilizes cotton fibers instead of asbestos fibers, along with other components in addition to Portland cement and silica. However, in the past it has been found that products containing fibrous asbestos substitutes do not have the desirable relatively low wet-to-dry shrinkage characteristics of an asbestos-cement composition, particularly the non-autoclave products, and the higher dimensional movement could result in undesirable exterior durability.